Welsh v. United States (1970) presented the Supreme Court with the problem of whether conscientious objector status had to be extended to a person who rejected participation in war as a matter of conscience, but who was an avowed atheist. When it ruled in Welsh’s favor, the Court offered the fullest answer it has yet given to a central constitutional problem: the definition of the “religion” which is protected by the First Amendment. This article, based on extensive interviews with Elliott Welsh, tells his story for the first time. It also sheds light on the perennial problem of discerning the boundaries of the free exercise clause.